The present invention generally relates to the recovery of data.
Data that has been conventionally saved as non-electronic data by using paper or film or the like is saved as electronic data and adopted in business as a result of the rapid development of an Internet society. In the computer system that saves and uses such data, the loss of data as a result of an unexpected accident or disaster or the like not only brings about stoppage of the computer system but also hinders the continuity of the business, which is a major problem.
In case of such a situation, the data of the storage system used in the computer system are saved to a tape or separate disk or the like at regular intervals. This processing is known as a ‘backup’. Further, the process whereby data of the storage system are restored using backup date saved by means of a backup to restore the computer system is called ‘recovery’.
Indicators that are used when running such a backup and recovery include a Recovery Time Objective (abbreviated to ‘RTO’ hereinbelow), a Recovery Point Objective (abbreviated to ‘RPO’ hereinbelow). An RTO is a target value for the time taken for recovery, that is, a target value for the time taken to restore the computer system by restoring data after the computer system has stopped. An RPO is an indicator that indicates how much data of the storage system can be restored to the data of the most recent time in cases where the computer system has stopped. The shortening of both the RPO and RTO are essential in the backup and recovery operation.
As a technology that is related to the backup and recovery of a storage system, Japanese Application Laid Open No. 2005-18738 is known. Japanese Application Laid Open No. 2005-18738 discloses a CDP (Continuous Data Protection) technology according to which the storage system accumulates journal data (also referred to as ‘JNL’ hereinbelow) each time the host computer writes data to a data volume of the storage system and shortens the RPO and RTO by using a JNL to restore the data of the data volume. As a result of this technology, even when an application that is running on the host computer is not equipped with a function for accumulating JNL, data are restored by means of JNL that the storage system has accumulated.
According to Japanese Application Laid Open No. 2005-18738, when a JNL volume in which JNL have accumulated is full, an old JNL (normally the JNL that was written at the oldest time) is overwritten with the JNL that is newly written. That is, the oldest restorable time is made current as the JNL volume is updated. Therefore, even when there is a desire to recover data at a time desired by the administrator, these data can sometimes not be recovered.
Furthermore, if the amounts of data written by applications to a data volume and the frequencies with which these data are written are different, because the JNL amounts accumulated per unit time vary, the speed of progress of the oldest restorable time is not limited to a fixed speed. Hence, it is difficult to manage to what extent data of a previous time can be restored.